/Engine/Plugins/Runtime/GameplayAbilities/Source/GameplayAbilities/Public/Abilities/GameplayAbilityTypes.h
How the ability is instanced when executed. This limits what an ability can do in its implementation. For example, a NonInstanced Ability cannot have state. It is probably unsafe for an InstancedPerActor ability to have latent actions, etc.
namespace EGameplayAbilityInstancingPolicy { enum Type { NonInstanced, InstancedPerActor, InstancedPerExecution, } }